The present invention relates to a mechanical actuating device for a spot-type disc brake comprising a brake caliper embracing the brake disc inwardly or outwardly, the brake caliper including at least one axial circular bore which incorporates therein a substantially cylindrical hollow brake piston acting on one brake shoe via an intermediate plate if necessary, an actuating spindle arranged axially in the brake piston and adapted to be turned around its axis by means of an actuating means, the actuating spindle cooperating with an actuating nut also disposed in the brake piston and abutting with its outer surface at least partly the inner wall of the one brake shoe such that the brake piston is advanced upon an axial relative displacement between the spindle and the nut caused by the actuating spindle being turned, and with an automatic adjusting device for the brake piston arranged likewise in the brake piston. The present invention refers in particular to a special design of a floating caliper brake, namely to a so-called fist-type caliper brake, in which one single bridge embraces the brake disc fist-like.
In a known spot-type disc brake adapted to be actuated both hydraulically and mechanically (German Patent DE-AS No. 15 75 996), the brake piston is located axially freely slidably on the actuating nut and is for actuation subjected from the inside to an adjusting spindle cooperating with the adjusting device. The known brake is composed by a comparatively great number of components, and the actuating force acts on the bottom of the brake piston through a surface of the adjusting spindle which is relatively small. The resetting of the adjusting device after a lining renewal is problematic. Construction and assembly of the known brake are also rather costly.